There has been a trend to erect slender and tall high rise buildings. Tall slender buildings are, by design and nature, more flexible than shorter buildings, allowing for more lateral movement in their upper stories. A building designed to resist all of these movements would be far too large to be feasible for design and construction (e.g. a Pyramid). In order to reduce cost and dead weight, such buildings are known to incorporate light-weight materials. One downside to the use of such light-weight materials in slender buildings is that the buildings become susceptible to vibrations. For example, long ceiling spans and other long structural members can vibrate at natural frequencies and exceed acceleration limits as a result of seismic loads, wind loads and human induced loads.
Tuned Mass Damper (TMD) systems are generally employed to reduce or eliminate gross oscillations of the building structure itself by providing structural damping. To some extent, TMDs can also be used to overcome the vibrations in the buildings. The use of TMDs is preferred over increasing the structural mass because more damping can be achieved with less mass using TMDs compared to simply increasing the structural mass.
TMDs typically include a mass suspended (e.g., near the top of the building) via cables and/or columns and coupled to the building structure via one or more damping systems. To operate effectively, the mass of the TMD must be allowed to move freely. However, friction forces located at joints between components of the TMD can impede such movement thereby reducing the effectiveness of the TMD.
Prior art ball and socket bearings are small (e.g., 1 to 2 inches nominal size) and typically are either designed to handle mostly radial loading, or are designed with little misalignment capacity.
Based on the foregoing, there is a need to provide an improved TMD in which the mass is allowed to move more freely than in prior art TMDs.